Method of cooling a fuel cell

ABSTRACT

A fuel cell is of a simple structure for preventing a partial temperature difference from being developed in a fuel cell structural body, and maintaining an effective operative area and performance.  
     The fuel cell  10  includes a plurality of fuel cells  20  each sandwiched between separators  40 , and has circulatory passages  29   a,    29   b  defined therein for circulating cooling water, which has been used to cool the fuel cells  20 , along opposite sides of electric generation sections  28  of the fuel cells  20.

TECHNICAL FIELD

[0001] The present invention relates to a fuel cell having an electrolyte membrane sandwiched between an anode electrode and a cathode electrode.

BACKGROUND ART

[0002] Solid polymer electrolyte fuel cell comprise a plurality of stacked fuel cell structural bodies (unit cells) each comprising an electrolyte membrane in the form of an ion exchange membrane and a catalytic electrode and a porous carbon electrode which are disposed one on each side of the electrolyte membrane, and a plurality of separators sandwiching the structural bodies.

[0003] Hydrogen supplied to the anode of the fuel cell is converted into hydrogen ions on the catalytic electrode, which move through the electrolyte membrane that has been humidified to an appropriate extent toward the cathode of the fuel cell. Electrons generated while the hydrogen ions are moving are transferred to an external circuit for use as direct-current electric energy. An oxygen containing gas such as an oxygen gas or air is supplied to the cathode electrode to generate water through a reaction between the hydrogen ions, the electrons, and the oxygen on the cathode electrode.

[0004] For such a fuel cell, there has been known a structure which, as shown in FIG. 11 of the accompanying drawings, comprises fuel cell structural bodies 2 and separators 4 which are alternately stacked together, each of the fuel cell structural bodies 2 having an electric generation section (electrode) 2 a which is supplied with cooling water in a direction parallel to the flow of a fuel gas, e.g., a hydrogen gas and an oxygen containing gas, e.g., an oxygen gas.

[0005] Since the cooling water flows vertically in the electric generation section 2 a, a relatively large temperature difference is developed between central and opposite side regions of the electric generation section 2 a due to thermal diffusion. Because of a drop in the temperature, moisture is condensed in the opposite side regions of the electric generation section 2 a, creating inoperative regions in the electric generation section 2 a. In addition, the electric generation section 2 a tends to have low-performance regions on account of the low temperature. As a result, the electric generation section 2 a has its effective operative area and performance greatly lowered.

[0006] It is an object of the present invention to provide a fuel cell which will solve the above problems and has a simple structure for preventing partial temperature differences from being developed in fuel cell structural bodies thereby to maintain an effective operative area and performance.

DISCLOSURE OF THE INVENTION

[0007] According to the present invention, a cooling medium, which has been used to cool an electric generation section of a fuel cell structural body, along outer sides of the electric generation section. Therefore, the cooling medium whose temperature has been increased by a heat exchange in the electric generation section flows outside of the electric generation section. Consequently, any temperature difference between a central region of the electric generation section and outer edges thereof is minimized, thereby preventing moisture condensation and increasing an effective operative area and performance of the electric generation section.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a fragmentary perspective view of a fuel cell according to the present invention;

[0009]FIG. 2 is an exploded perspective view of the fuel cell;

[0010]FIG. 3 is a front elevational view of an electric generation section of the fuel cell;

[0011]FIG. 4 is a front elevational view of a gasket of the fuel cell;

[0012]FIG. 5 is a front elevational view of a first manifold plate of the fuel cell;

[0013]FIG. 6 is a front elevational view of a second manifold plate of the fuel cell;

[0014]FIG. 7 is a front elevational view of a surface pressure generating plate of the fuel cell;

[0015]FIG. 8 is a front elevational view of a separator body of the fuel cell;

[0016]FIG. 9 is a diagram illustrative of a lateral temperature distribution in the electric generation section of the fuel cell;

[0017]FIG. 10 is a fragmentary perspective view of a fuel cell, showing another arrangement of circulatory passages; and

[0018]FIG. 11 is a diagram illustrative of a lateral temperature distribution in an electric generation section of a conventional fuel cell.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] As shown in FIGS. 1 and 2, a fuel cell according to the present invention basically comprises a horizontal stack of fuel cells (fuel cell structural bodies) 20. Each of the fuel cells 20 includes an electric generation section 28 which comprises an anode electrode 26 and a cathode electrode 24 which sandwich a solid polymer electrolyte membrane 22 therebetween. The electric generation section 28 is described in detail in International laid-open publication WO94-15377, which is incorporated herein by reference. In FIG. 2, the solid polymer electrolyte membrane 22, the anode electrode 26, and the cathode electrode 24 are separate from each other. However, they may be of an integral structure.

[0020] As shown in FIG. 3, the solid polymer electrolyte membrane 22 has an oblong hole 22 a for passing a fuel gas such as a hydrogen gas or the like in one direction, a hole 22 b for passing cooling water, and a hole 22 c for passing an oxygen containing gas, e.g., an oxygen gas, the holes 22 a, 22 b, 22 c being defined in an upper portion of the solid polymer electrolyte membrane 22. The solid polymer electrolyte membrane 22 also has a hole 22 d for passing the fuel gas, a hole 22 e for passing the cooling water, and a hole 22 f for passing the oxygen containing gas, the holes 22 d, 22 e, 22 f being defined in a lower portion of the solid polymer electrolyte membrane 22. The solid polymer electrolyte membrane 22 further has holes 23 a-23 c, 23 d-23 f defined in opposite side regions thereof and providing circulatory passages 29 a, 29 b for circulating the cooling water (cooling medium) which has been used to cool the electric generation section 28 along outer edges of the electric generation section 28.

[0021] A first gasket 30 and a second gasket 32 are disposed one on each side of the electric generation section 28. As shown in FIG. 4, the first gasket 30 has a large opening 34 for accommodating the cathode electrode 24 therein, and the second gasket 32 has an opening 36 for accommodating the anode electrode 26. As with the solid polymer electrolyte membrane 22, the first gasket 30 has holes 30 a, 30 d for passing the fuel gas, holes 30 b, 30 e for passing the cooling water, and holes 30 c, 30 f for passing the oxygen containing gas, these holes being defined respectively in upper and lower end portions of the first gasket 30. The first gasket 30 also has holes 31 a-31 c, 31 d-31 f defined in opposite side regions thereof and serving as the circulatory passages 29 a, 29 b. The second gasket 32 is of the same structure as the first gasket 30.

[0022] The fuel cell 20 is sandwiched by separators 40. As shown in FIG. 2, each of the separators 40 comprises a first manifold plate 42, a first surface pressure generating plate 44 held against the first manifold plate 42, a second surface pressure generating plate 46, a separator body 48 sandwiched between the first surface pressure generating plate 44 and the second surface pressure generating plate 46, a second manifold plate 50 held against the second surface pressure generating plate 46.

[0023] As shown in FIG. 5, the first manifold plate 42 comprises a rectangular flat plate, and has a fuel gas supply recess 42 a defined in an upper right corner thereof for supplying the fuel gas and a cooling water discharge hole 42 b defined therein adjacent to the fuel gas supply recess 42 a for discharging the cooling water. The first manifold plate 42 also has an oxygen containing gas supply hole 42 c defined in an upper left corner thereof for supplying the oxygen containing gas, and a fuel gas discharge recess 42 d defined in a lower left corner thereof for discharging the fuel gas. The first manifold plate 42 further has a cooling water supply hole 42 e and an oxygen containing gas discharge hole 42 f defined therein and spaced successively from the fuel gas discharge recess 42 d toward a lower right corner thereof. The fuel gas supply recess 42 a and the fuel gas discharge recess 42 d are held in communication with each other through an opening 45 which accommodates a fuel gas flow rectifying plate 80, described later on. The first manifold plate 42 also has holes 43 a-43 c, 43 d-43 f defined in opposite side regions thereof and serving as the circulatory passages 29 a, 29 b.

[0024] As shown in FIG. 6, the first manifold plate 42 and the second manifold plate 50 are basically of a symmetrical structure. Therefore, details of the second manifold plate 50 will not be described in detail below. The second manifold plate 50 has a fuel gas supply hole 50 a, a cooling water discharge hole 50 b, and an oxygen containing gas supply recess 50 c, which are defined in an upper portion thereof, and a fuel gas discharge hole 50 d, a cooling water supply hole 50 e, and an oxygen containing gas discharge recess 50 f, which are defined in a lower portion thereof. The oxygen containing gas supply recess 50 c and the oxygen containing gas discharge recess 50 f are held in communication with each other through an opening 52 which accommodates an oxygen containing gas flow rectifying plate 82, described later on. The second manifold plate 50 also has holes 51 a-51 c, 51 d-51 f defined in opposite side regions thereof and serving as the circulatory passages 29 a, 29 b.

[0025] As shown in FIG. 7, the first surface pressure generating plate 44 that is held against the first manifold plate 42 comprises a flat plate made of an electrically conductive material or is formed integral with or made of the same material as the fuel gas flow rectifying plate 80, described later on. The first surface pressure generating plate 44 has a fuel gas supply communication hole 44 a held in communication with the fuel gas supply recess 42 a in the first manifold plate 42, a cooling water discharge communication hole 44 b held in communication with the cooling water discharge hole 42 b, and a communication hole 44 c held in communication with the oxygen containing gas supply hole 42 c, the holes 44 a, 44 b, 44 c being defined in an upper portion of the first surface pressure generating plate 44. The first surface pressure generating plate 44 further has a communication hole 44 d held in communication with the fuel gas discharge recess 42 d in the first manifold plate 42, and a communication hole 44 e held in communication with the cooling water supply hole 42 e, and a communication hole 44 f held in communication with the oxygen containing gas discharge hole 42 f. The first surface pressure generating plate 44 also has holes 57 a-57 c, 57 d-57 f defined in opposite side regions thereof and held in communication with the holes 43 a-43 c, 43 d-43 f in the first manifold plate 42. The second surface pressure generating plate 46 is of essentially the same structure as the first surface pressure generating plate 44, and will not be described in detail below.

[0026] The separator body 48, as a third manifold plate, serves to supply cooling water upwardly to cool the electric generation section 28. As shown in FIG. 8, the separator body 48, which is relatively thick, is made of an electrically conductive dense material (solid). The separator body 48 has a fuel gas supply hole 48 a defined in an upper right corner thereof and held in communication with the recess 42 a in the first manifold plate 42 and the communication hole 44 a in the first surface pressure generating plate 44, for supplying the fuel gas. The separator body 48 also has a cooling water discharge recess 48 b defined in a substantially central upper portion thereof adjacent to the fuel gas supply hole 48 a and held in communication with the cooling water discharge hole 42 b in the first manifold plate 42 and the communication hole 44 b in the first surface pressure generating plate 44. The separator body 48 further has an oxygen containing gas supply hole 48 c defined in an upper left corner thereof and held in communication with the oxygen containing gas supply hole 42 c in the first manifold plate 42 and the communication hole 44 c in the first surface pressure generating plate 44.

[0027] The separator body 48 also has a hole 48 d defined in a lower left corner thereof and held in communication with the fuel gas discharge recess 42 d in the first manifold plate 42 and the communication hole 44 d in the first surface pressure generating plate 44, and a cooling water supply recess 48 e directly below the cooling water discharge recess 48 b. The separator body 48 also has an oxygen containing gas discharge hole 48 f defined in a lower right corner thereof. The recesses 48 b, 48 e communicate with each other through a large opening 62. The separator body 48 further has holes 49 a-49 c, 49 d-49 f defined in opposite side regions thereof and held in communication with the holes 43 a-43 c, 43 d-43 f in the first manifold plate 42 and the holes 57 a-57 c, 57 d-57 f in the first surface pressure generating plate 44.

[0028] Cooling water flow rectifying plates 70, 72 are fitted and fixed in the opening 62 in the separator body 48. The combined thickness of the cooling water flow rectifying plates 70, 72 is essentially the same as the thickness of the separator body 48. The cooling water flow rectifying plate 70 has a plurality of parallel grooves 70 a extending vertically in FIG. 2. Likewise, the cooling water flow rectifying plate 72 has a plurality of parallel grooves 72 a. When the cooling water flow rectifying plates 70, 72 are combined with each other, the grooves 70 a, 72 a jointly define large cooling water flow rectifying passages (cooling passages) which are held in communication with the recess cooling water discharge recess 48 b and the cooling water supply recess 48 e, respectively.

[0029] As shown in FIG. 2, the fuel gas flow rectifying plate 80 is fitted in the opening 45 in the first manifold plate 42. The fuel gas flow rectifying plate 80 has a flat surface and an opposite surface having a plurality of parallel grooves 80 a defined therein and extending vertically. The parallel grooves 80 a provide communication between the fuel gas supply recess 42 a and the fuel gas discharge recess 42 d.

[0030] The oxygen containing gas flow rectifying plate 82 is fitted in the opening 52 in the second manifold plate 50. The oxygen containing gas flow rectifying plate 82 has a flat surface and an opposite surface having a plurality of parallel grooves 82 a defined therein and extending vertically. The parallel grooves 82 a provides communication between the oxygen containing gas supply recess 50 c and the oxygen containing gas discharge recess 50 f. The thickness of the first manifold plate 42 and the fuel gas flow rectifying plate 80, and the thickness of the second manifold plate 50 and the oxygen containing gas flow rectifying plate 82 are essentially the same as each other.

[0031] The separator body 48 thus constructed is sandwiched by the first surface pressure generating plate 44 and the second surface pressure generating plate 46, which are in turn sandwiched by the first manifold plate 42 and the second manifold plate 50. The second gasket 32 is held against the first manifold plate 42, and the first gasket 30 is held against the second manifold plate 50, with the electric generation section 28 sandwiched between the gaskets 30, 32, thus making up the fuel cell 20.

[0032] Many fuel cells 20, each comprising the first manifold plate 42 with the flow rectifying plate 80 assembled therein, the second gasket 32, the anode electrode 26, the solid polymer electrolyte membrane 22, the cathode electrode 24, the first gasket 30, the second manifold plate 50 with the flow rectifying plate 82 assembled therein, the second surface pressure generating plate 46, the separator body 48 with the flow rectifying plates 70, 72 assembled therein, and the first surface pressure generating plate 44, which are arranged in the direction indicated by the arrow in FIG. 2, are stacked together. One end of the stack is held against a first end plate 84, and the other end of the stack is held against a second end plate 86. The first and second end plates 84, 86 are fastened to each other by stud bolts 87 (see FIG. 1).

[0033] The first end plate 84 has a groove 84 a defined therein for dividing the cooling water into left and right flows, the groove 84 a facing the cooling water discharge hole 42 b in the first manifold plate 42. The groove 84 a has opposite ends facing the holes 43 a, 43 d in the first manifold plate 42. The first end plate 84 has grooves 84 b, 84 c defined in respective opposite regions thereof and providing communication between the holes 43 b, 43 c in the first manifold plate 42 and also between the holes 43 e, 43 f therein. The first end plate 84 further has a through hole 84 d defined therein for introducing the oxygen containing gas and a through hole 84 e defined therein for discharging the oxygen containing gas.

[0034] The second end plate 86 has a through hole 86 a defined therein and held in communication with the fuel gas supply hole 50 a in the second manifold plat 50, for supplying the fuel gas, a through hole 86 b defined therein and held in communication with the cooling water supply hole 50 e, a through hole 86 c defined therein and held in communication with the fuel gas discharge hole 50 d, and through holes 86 d, 86 e defined therein and held in communication with the holes 51 c, 51 f (see FIG. 2). The second end plate 86 also has grooves 88 a, 88 b defined in an inner surface thereof which faces the second manifold plate 50 and providing communication between the holes 51 a, 51 b in the second manifold plate 50 and also between the holes 51 d, 51 e therein.

[0035] Operation of the fuel cell 10 thus constructed will be described below.

[0036] Plural fuel cells 20 are sandwiched between separators 40, stacked such that their communication holes, holes, and recesses held in communication with each other, and fixed by the first and second end plates 84, 86.

[0037] When the fuel gas (hydrogen gas) is supplied from the through hole 86 a in the second end plate 86 into the fuel cell 10, the fuel gas is supplied from the fuel gas supply hole 50 a in the second manifold plate 50 into the fuel gas supply recess 42 a in the first manifold plate 42, and then supplied through the grooves 80 a in the fuel gas flow rectifying plate 80 disposed in the opening 45 held in communication with the fuel gas supply recess 42 a, to the anode electrode 26 of the electric generation section 28.

[0038] The oxygen containing gas (air) is supplied from the through hole 84 d in the first end plate 84 into the fuel cell 10, and flows through the oxygen containing gas supply hole 42 c in the first manifold plate 84 and the oxygen containing gas supply hole 48 c in the separator body 48 into the oxygen containing gas supply recess 50 c in the second manifold plate 50. The oxygen containing gas passes from the oxygen containing gas supply recess 50 c through the grooves 82 a in the oxygen containing gas flow rectifying plate 82 to the cathode electrode 24.

[0039] An unused fuel gas is discharged through the fuel gas discharge recess 42 d in the first manifold plate 42 out of the fuel cell 10 from the through hole 86 c in the second end plate 86. An unused oxygen containing gas is discharged through the oxygen containing gas discharge recess 50 f in the second manifold plate 50 out of the fuel cell 10 from the through hole 84 e in the first end plate 84.

[0040] The cooling water is supplied from the through hole 86 b in the second end plate 86 into the fuel cell 10, and flows through the cooling water supply hole 50 e in the second manifold plate 50 into the cooling water supply recess 48 e in the separator body 48. The cooling water then flows upwardly along the cooling water flow rectifying passages defined between the cooling water flow rectifying plate 70, 82 fixedly fitted in the opening 62 in the separator body 48, absorbs heat generated by the electric generation section 28, thereby cooling the electric generation section 28, and thereafter flows from the cooling water discharge recess 48 b in the separator body 48 toward the first end plate 84.

[0041] The cooling water which has been used to remove the heat from the electric generation section 28 flows from the groove 84 a in the first end plate 84 through the circulatory passages 29 a, 29 b, and is discharged out of the fuel cell 10 from the through holes 86 d, 86 e in the second end plate 86. Therefore, the cooling water introduced in the groove 84 a in the first end plate 84 is supplied to the holes 43 a, 43 d in the first manifold plate 42 which serve as the circulatory passages 29 a, 29 b.

[0042] The cooling water supplied into the hole 43 a in the first manifold plate 42 flows through the hole 49 a in the separator body 48 and the hole 51 a in the second manifold plate 50 into the groove 88 a in the second end plate 86. The cooling water is then introduced through the hole 51 b in the second manifold plate 50 which is held in communication with the groove 88 a, the hole 49 b in the separator body 48, and the hole 43 b in the first manifold plate 42 into the groove 84 b in the first end plate 84. Therefore, the cooling water flows from the groove 84 b through the hole 43 c in the first manifold plate 42, the hole 49 c in the separator body 48, and the hole 51 c in the second manifold plate 50, and is discharged out of the fuel cell 10 from the through hole 86 d in the second end plate 86.

[0043] The cooling water which has been supplied from the groove 84 a in the first end plate 84 into the circulatory passage 29 b flows through the hole 43 d in the first manifold plate 42, the hole 49 d in the separator body 48, and the hole 51 d in the second manifold plate 50 into the groove 88 b in the second end plate 50, and thereafter returns through the holes 51 e, 49 e, 43 e into the groove 84 c in the first end plate 84. The cooling water is discharged through the holes 43 f, 49 f, 51 f which are held in communication with the groove 84 c out of the fuel cell 10 from the through hole 86 e in the second end plate 86.

[0044] In this embodiment, as described above, the cooling water which has been supplied to the fuel cell 10 and removed the heat from the electric generation section 28 circulates along the circulatory passages 29 a, 29 b on the opposite sides of the electric generation section 28. Consequently, on the opposite sides of the electric generation section 28, the cooling water whose temperature has been increased by a heat exchange in the electric generation section 28 flows along the circulatory passages 29 a, 29 b for thereby preventing the electric generation section 28 in the vicinity of its opposite ends from being lowered in temperature (see FIG. 9).

[0045] As a consequence, any temperature difference between a central region of the electric generation section 28 and opposite edges thereof is minimized, thereby preventing moisture condensation on the opposite edges of the electric generation section 28 due to a temperature drop. Therefore, the electric generation section 28 is free of inoperative regions which would otherwise be caused by moisture condensation, and any low-performance regions of the electric generation section 28 due to low temperatures are reduced. Thus, the effective operative area and performance of the electric generation section 28 are effectively increased.

[0046] According to this embodiment, furthermore, the fuel cell 10 is only required to have the circulatory passages 29 a, 29 b therein for circulating the cooling water which has absorbed heat through a heat exchange along the opposite outer sides of the electric generation section 28. The fuel cell 10 is not complicated in overall structure, and can easily and economically be designed.

[0047] In the present embodiment, the circulatory passages 29 a, 29 b pass three times on the opposite sides of the electric generation section 28 (one and a half reciprocating cycle on each side). However, the fuel cell 10 may have circulatory passages 90 a, 90 b shown in FIG. 10. The circulatory passages 90 a, 90 b are provided by oblong holes 92 a, 92 b defined as vertically elongate holes in respective opposite sides of the second manifold plate 50. The first manifold plate 42, the second gasket 32, the solid polymer electrolyte membrane 22, the first gasket 30, the second surface pressure generating plate 46, the separator body 48, and the first surface pressure generating plate 44 have vertically elongate oblong holes (not shown) defined in opposite sides thereof and held in communication with each other.

[0048] The circulatory passages 90 a, 90 b circulate cooling water, which has been used to remove heat from the electric generation section 28 and sent to the first end plate 84, through the vertically elongate oblong holes 92 a, 92 b, and then discharge the cooling water out of the fuel cell 10. Therefore, the circulatory passages 90 a, 90 b are capable of regulating the temperatures of the opposite sides of the electric generation section 28 together in the vertical direction, and also offer the same advantages as those of the circulatory passages 29 a, 29 b.

[0049] Industrial Applicability:

[0050] In the fuel cell according to the present invention, a cooling medium whose temperature is relatively high due to a heat exchange at an electric generation section is circulated along the outer sides of the electric generation section to prevent a partial temperature difference from being developed in the electric generation section. Therefore, moisture condensation is prevented, and the effective operative area and performance of the electric generation section are increased. 

1. A fuel cell comprising: a fuel cell structural body 20 having a solid polymer electrolyte membrane 22 sandwiched between an anode electrode 26 and a cathode electrode 24; and separators 40 sandwiching said fuel cell structural body 20; the fuel cell 10 having therein a cooling passage for cooling an electric generation section 28 of said fuel cell structural body 20, and circulatory passages 29 a, 29 b for circulating a cooling medium which has been used to cool said electric generation section 28 along outer sides of said electric generation section
 28. 2. A fuel cell according to claim 1 , wherein said cooling passage is arranged to supply said cooling medium vertically to said electric generation section 28, and said circulatory passages 29 a, 29 b are arranged to circulate the cooling medium along opposite outer sides of said electric generation section
 28. 3. A fuel cell according to claim 1 or 2 , wherein said circulatory passages 29 a, 29 b are arranged to pass said cooling medium along the outer sides of said electric generation section 28 in at least one reciprocating cycle.
 4. A fuel cell according to claim 1 or 2 , wherein said circulatory passages 29 a, 29 b comprise oblong holes 92 a, 92 b elongate in a direction across the direction in which the cooling medium flows, in order to pass said cooling medium only once along the outer sides of said electric generation section
 28. 5. A fuel cell according to claim 1 or 2 , further comprising: a pair of end plates 84, 86 disposed on opposite ends of the fuel cell 10; said end plates 84, 86 having grooves 84 a-84 c, 88 a, 88 b defined therein for supplying a used cooling medium which has flowed through said cooling medium to said circulatory passages 29 a, 29 b. 